Oct 22 (Reuters) - U.S. energy company Energy Transfer LP said on Monday it plans to put its $2.5 billion Sunoco Mariner East 2 natural gas liquids pipeline in Pennsylvania into service soon:

* "Mariner East 2 will be put into service shortly, once it is mechanically complete," Energy Transfer spokeswoman Lisa Dillinger told Reuters in an email.

* Earlier Monday, analysts at Height Capital Markets in Washington, DC, said the pipeline would enter service in the next few weeks.

* The company had previously told some customers that it planned to finish the project in the fourth quarter. These include U.S. energy producer Range Resources Corp and U.S. shipping company Dorian LPG Ltd, which owns very large gas carriers (VLGCs).

* When Energy Transfer's Sunoco subsidiary started building the $2.5 billion Mariner East 2 in February 2017, the company expected to finish the project by the third quarter of 2017.

* Mariner East 2, however, has been slowed by numerous work stop orders in Pennsylvania due primarily to drilling fluid spills during horizontal drills under obstacles like rivers and highways.

* The Mariner East project transports liquids from the Marcellus and Utica shale fields in western Pennsylvania to customers in the state and elsewhere, including international exports from ETP's Marcus Hook complex near Philadelphia.

* Mariner East 1 started service in the 1930s transporting refined products from the Philadelphia area to western Pennsylvania. It was repurposed and expanded to transport propane in 2014 and ethane in 2016 from western Pennsylvania to customers in the eastern part of the state.

* Mariner East 2 will boost capacity of the Mariner East project from 70,000 barrels per day (bpd) to 345,000 bpd and open the pipeline to suppliers in Ohio and West Virginia. Mariner East 2X, which Energy Transfer has said is expected to enter service in the third quarter of 2019, will add another 250,000 bpd.